1. Field of the Invention
This invention relates to the field of all-optical processing.
2. Technical Background
In the field of all-optical processing, optical signal streams are used for data processing applications. These optical streams consist of an optical pulse train that is divided into a series of bit slots. Each bit slot, which has a predetermined length within the pulse train, represents a single bit of data, with, for example, the presence or absence of an optical pulse within a bit slot representing complementary logical states. Thus, for example, the presence of a pulse may represent a binary “1”, whilst the absence of a pulse may represent a binary “0”, or vice versa.
It has long been a goal to produce devices capable of carrying out all optical processing. WO 99/14649 describes a ‘bit serial’ method and circuit which can perform serial calculations on sequential bits of an optical packet header to compare this with a locally generated word and divert the packet according to whether the header and word are identical or different. These circuits include optical signal feedback paths of a length equivalent to a 1-bit delay. Provided such feedback paths can be constructed, this method could be used for the purposes of address recognition in the time taken for receipt of the whole packet, ie ‘on the fly’ without danger of contention with a succeeding packet. For high-speed operation, the feedback path length must be short. For example, at a bit rate of 40 Gbit/s, a 1-bit delay requires a path length of 5 mm in silica, or about 2 mm in semiconductor. Such hardware devices are not yet readily implemented.
WO 99/49600 describes a circuit which uses ‘bit differential processing’ to determine the parity of a binary word. The circuit carries out a series of operations between sequential copies of the binary word with the result from the previous operation, the parity of the binary word being indicated by sequential bits of the resultant word. Unlike the serial packet receiver described in WO 99/14649, this circuit can be readily implemented, as it uses a multiple-bit optical regenerative memory having longer delay paths.